How to enable Firefox WebExtensions on Mozilla websites (in https://www.ghacks.net/2017/10/27/how-to-enable-firefox-webextensions-on-mozilla-websites/):
- Load about:config in the Firefox web browser.
- You can run a search for just to make sure it does not exist:
privacy.resistFingerprinting.block_mozAddonManager.
It does not in the most recent Firefox Nightly builds at the time of writing.
- Right-click in the part of the window that lists the preferences, and select New > Boolean from the context menu.
- Name the new Boolean value:
privacy.resistFingerprinting.block_mozAddonManager.
- Set its value to true.

This only toggles in the address bar:
- Go to "about:config"
- set `security.insecure_password.ui.enabled` to false.
For the inline floaters Security Nag:
- Go to "about:config"
- Set "security.insecure_field_warning.contextual.enabled" to false

About the hidden about:config command present in Firefox.
This command is executed in Firefox addressbar and opens the secret Preferences Manager
which allows you to change so many hidden settings in Firefox which are not available in Firefox Options window.
about:config not only allows you enable/disable many options in Firefox ,
but also allows you to reveal many hidden secret features in Firefox
which are not even documented by Mozilla developers.